The present invention relates to an image forming apparatus.
In a conventional image forming apparatus such as a printer, a copier, a facsimile, and the likes, a charge roller charges a surface of a photosensitive drum, and an LED (Light Emitting Diode) head exposes the surface of the photosensitive drum to form a static latent image thereon. Then, a developing roller attaches a thin layer of toner to the static latent image through static electricity, thereby forming a toner image. A transfer roller transfers the toner image to a sheet.
After the transfer roller transfers the toner image to the sheet, a cleaning device removes toner remaining on the photosensitive drum, so that toner is collected in a waste toner container disposed in a toner cartridge.
After the sheet is picked up from a sheet supply unit, the sheet is transported to a transfer portion between the photosensitive drum and the transfer roller, so that the toner image is transferred to the sheet at the transfer portion, thereby forming the toner image on the sheet. Then, the sheet is transported to a fixing device, so that the fixing device fixes the toner image to the sheet, thereby forming an image on the sheet. Afterward, first and second discharge rollers of a sheet discharge unit disposed at a downstream side of the fixing device discharge the sheet to outside the printer, or outside the apparatus.
In the conventional printer, when images are formed on both sides of the sheet, an image is formed on a front side of the sheet first. After the sheet passes through the fixing device, the first and second discharge rollers transport the sheet. After a front edge of the sheet passes through the second discharge roller and a rear end of the sheet passes through the second discharge roller, the second discharge roller rotates in a reverse direction, thereby transporting the sheet to a reverse path.
After the sheet passes through the reverse path, the sheet is transported to the transfer portion one more time. Then, the toner image is formed on a backside of the sheet, and the toner image is fixed, thereby forming an image on the backside of the sheet.
In the conventional printer, the sheet discharge unit is arranged to discharge the sheet in various ways according to a material of the sheet, a thickness of the sheet, and the likes. For example, when an ordinary sheet is used as the sheet, the sheet discharge unit discharges the ordinary sheet while a side thereof with an image formed thereon faces downwardly, or the sheet discharge unit performs face down sheet discharge.
On the other hand, when a cardboard is used, it is necessary to provide a straight transportation path on a downstream side of the fixing device. Accordingly, the sheet discharge unit discharges the sheet while a side thereof with an image formed thereon faces upwardly, or the sheet discharge unit performs face up sheet discharge.
In the conventional printer, the sheet discharge unit is provided with a sheet placing tray as a medium placing tray having a sheet guide portion disposed to be freely rotatable with respect to a main body of the conventional printer or an apparatus main body. When the sheet discharge unit performs the face down sheet discharge, the sheet placing tray is closed with respect to the apparatus main body.
In this case, after the image is formed on the sheet at the transfer portion, the sheet passes through the fixing device and the first discharge roller transports the sheet. At this time, as described above, the sheet placing tray is closed with respect to the apparatus main body. The sheet is guided with the sheet guide portion disposed on the sheet placing tray and a transportation guide disposed on a downstream side of the sheet guide portion. Then, the second discharge roller discharges the sheet outside the apparatus, so that the sheet is placed on a sheet placing portion formed on a top portion of the apparatus main body.
When the sheet discharge unit performs the face up sheet discharge, the sheet placing tray is opened with respect to the apparatus main body. In this case, after the image is formed on the sheet at the transfer portion, the sheet passes through the fixing device, and the first discharge roller discharges the sheet outside the apparatus. Since the sheet placing tray is opened with respect to the apparatus main body, the sheet is placed on the sheet placing tray (refer to Patent Reference).
Patent Reference Japan Patent Publication No. 2002-104707
In the conventional printer, as described above, when the sheet discharge unit performs the face up sheet discharge, the sheet placing tray is opened with respect to the apparatus main body. After the first discharge roller transports the sheet, the sheet is directly transported to the sheet placing tray, not to the second discharge roller. Accordingly, even when the second discharge roller rotates, the sheet is not transported to the reverse path, so that the duplex printing is not performed.
In view of the problem described above, an object of the invention is to provide an image forming apparatus, in which it is possible to solve the problems of the conventional printer. In the image forming apparatus of the present invention, even when a sheet placing tray is opened with respect to an apparatus main body for performing the face up sheet discharge, it is possible to perform the duplex printing.
Further objects of the invention will be apparent from the following description of the invention.